This invention relates to an improvement in a pushbutton switch for use on an electronic apparatus or the like.
In a keyboard of a small size-electronic computer, for example, a push button switch having a movable contact is mounted on a printed circuit board or substrate having a fixed contact. When the push-button switch is depressed by the operator's finger pressure, the movable contact is brought into contact with the fixed contact to close the electrical circuit connected to the fixed contact. The pushbutton switch shown in FIG. 1 is used for such purpose. In FIG. 1, reference numeral 1 denotes a main member of the pushbutton switch. Reference numerals 2, 3 denote a pushbutton portion and a skirt portion of the main member 1, respectively. The pushbutton 2 and the skirt portion 3 consist of an insulating resilient material such as rubber and are formed integrally with each other, as may be seen from the drawing.
A movable contact 4 made of resilient conducting material is secured on a printed circuit board or substrate 5 below the pushbutton portion 2. A fixed contact 6 is provided on the substrate and forms a portion of a circuit pattern, not shown, of the substrate 5. In the above construction of the pushbutton switch, when finger pressure is applied to the push button portion 2 of the main member 1, the pushbutton portion 2 is deformed at an upstanding wall thereof so that the movable contact 4 is brought into contact with the fixed contact 6 to close the electrical circuit wire to contact 6. However, the prior-art pushbutton switch has the following defect. Assume that the movable contact 4 has been contacted with the fixed contact by a finger placed on the pushbutton portion 2. If the finger pressure is applied slightly off-center as indicated by the arrow mark in FIG. 2, the contact 4 tends to tilt because of the resilient properties of the main member 1 of the pushbutton switch. Thus there is a tendency for the current flowing through the contacts to be interrupted because of a poor electrical connection. If the finger pressure acts on the pushbutton portion 2 diagonally, the latter is deformed transversely and causes both transverse and oblique displacement of the movable contact 4, so that the movable contact will be brought into only partial contact with the fixed contact 6, again resulting in an insufficient electrical connection. The foregoing phenomena causing displacement or tilting of the movable contact 4 with respect to the fixed contact 6 also occur when the finger is placed not at the center but at the periphery of the pushbutton portion 2.
In addition, the prior-art pushbutton switch may be deformed or leveled in a skewed manner depending on the direction in which finger pressure is exerted upon the pushbutton portion. Hence, the switch may catch on a guide member which receives the pushbutton switch and may not close the contacts despite sustained finger pressure. The likely result would be an input error.